This specification relates to content item searching and retrieval.
Publications (e.g., electronic publications, websites, mobile applications, Internet browser applications, IPTV, digital video, etc.) may include third party content items (e.g., advertisements), for example, to financially support a resource provider's (e.g., publication provider) operations. Some resource providers do not maintain a third party content infrastructure, and thus depend on content serving entities to recruit third party content sponsors (e.g., advertisers, etc.) and to serve the sponsored content items.